feat(fluentd): add StatefulSet enhancements and headless service support

[yuvalcohenrise]

Summary

This PR adds several enhancements to the fluentd chart, primarily focused on improving StatefulSet deployments:

New Features

1. Headless Service Support

   • Added new headlessService configuration to enable headless services for StatefulSet deployments
   • Enables direct pod DNS resolution (e.g., pod-0.fluentd-headless.namespace.svc.cluster.local)
   • Configurable annotations and additional ports

2. PersistentVolumeClaimRetentionPolicy Support

   • Added persistentVolumeClaimRetentionPolicy configuration for StatefulSets
   • Allows control over PVC retention when pods are deleted or scaled down

3. PodDisruptionBudget (PDB) Support

   • Added new pdb.yaml template
   • Configurable minAvailable and maxUnavailable settings
   • Helps ensure availability during voluntary disruptions

4. HPA Support for StatefulSet

   • Extended HorizontalPodAutoscaler to work with StatefulSet (previously only Deployment)
   • Dynamic kind reference based on .Values.kind

5. Conditional Replicas for StatefulSet

   • StatefulSet replicas field is now only set when autoscaling is disabled
   • Prevents conflicts between HPA and static replica count

Changed Files

File	Change
charts/fluentd/values.yaml	Added persistentVolumeClaimRetentionPolicy, podDisruptionBudget, and headlessService configurations
charts/fluentd/templates/statefulset.yaml	Added conditional replicas and persistentVolumeClaimRetentionPolicy support
charts/fluentd/templates/hpa.yaml	Extended to support both Deployment and StatefulSet kinds
charts/fluentd/templates/pdb.yaml	New template for PodDisruptionBudget
charts/fluentd/templates/headless-service.yaml	New template for headless service
charts/fluentd/README.md	Added documentation for headless service

Example Usage

# Enable headless service for StatefulSet
headlessService:
  enabled: true
  annotations: {}
  ports:
    - name: "forwarder"
      protocol: TCP
      containerPort: 24224

# Configure PVC retention policy
persistentVolumeClaimRetentionPolicy:
  whenDeleted: Delete
  whenScaled: Delete

# Enable PodDisruptionBudget
podDisruptionBudget:
  enabled: true
  minAvailable: 1

# Enable HPA for StatefulSet
kind: StatefulSet
autoscaling:
  enabled: true
  minReplicas: 2
  maxReplicas: 10
  targetCPUUtilizationPercentage: 80

[patrick-stephens]

Please can you rebase on the latest versions so we can bring in the updated CI?

[yuvalcohenrise]

@patrick-stephens Done